1. Field of the Invention
The present invention generally relates to digital audio and video (A/V) apparatuses, and more particularly, to a method for reducing channel changes times and maintaining synchronization between audio and video content during a channel change event in a digital A/V apparatus.
2. Background Information
In a digital television broadcast system, allowing viewers to change channels rapidly is an important feature. There are at least two major sources that contribute to channel change delay. The first source is from the group of picture (GOP) structure used by many video compression standards, such as MPEG-2 and H. 264. In a GOP, pictures are encoded using either intra or inter coding. An intra coded (I) picture (a.k.a., frame) uses information within itself for compression, and therefore can be decoded alone. Inter-coded pictures (i.e., B or P pictures), however, must be decoded after the related intra coded pictures (I picture) are decoded. Since I pictures typically require 3 to 10 times more bits than a B or P picture, they are encoded much less frequently in the bit stream in order to reduce the overall bit rate. In a digital television broadcast system, I frames may only appear once every 1 to 2 seconds. When a digital A/V apparatus tunes to a program, it must wait until the first I frame is received before any picture can be decoded or displayed. This may cause a significant delay.
The second source for channel change delay is from processing components in the digital A/V apparatus (e.g., set-top box (SIB)). In an internet protocol television (IPTV) broadcast system, for example, various active components in the transport network may contribute jitter to the media streams. This jitter has to be reduced at the digital A/V apparatus to avoid presenting unpleasant artifacts to the users. Reducing such jitter at the digital A/V apparatus is typically accomplished through a buffering process, which can be a major source of delay in rendering video content during a channel change event. Since human beings tend to be more sensitive to audio jitter than to video jitter, received audio content generally needs to be more strongly de-jittered at the digital A/V apparatus. Stronger de-jittering for audio content leads to longer buffering, longer channel change times, and a potential for losing synchronization between audio and video content during a channel change event.
Accordingly, there is a need for a method for reducing channel changes times and maintaining synchronization between audio and video content during a channel change event in a digital A/V apparatus. The present invention addresses these and/or other issues.